Method of inhibiting cavitation-erosion corrosion of aluminum surfaces using carboxylic acid based compositions comprising polymerizable-acid graft polymers

ABSTRACT

This invention relates to a method of inhibiting the cavitation-erosion corrosion of aluminum surfaces. The method comprises the step of contacting the aluminum surface with a formulation comprising a corrosion inhibitor composition comprising one or more carboxylic acids, or salts or isomers thereof, and a polymerizable-acid graft polymer which comprises an unsaturated grafting acid and an alkylene oxide polymer, or copolymers thereof. This method has been demonstrated to be a surprisingly effective means to inhibit cavitation-erosion corrosion of aluminum surfaces found in the cooling systems of internal combustion engines.

FIELD OF THE INVENTION

The present invention relates generally to a method of inhibitingcavitation-erosion corrosion of aluminum surfaces. More particularly,the present invention relates to the use of carboxylic acid basedcompositions comprising polymerizable-acid graft polymers in antifreezecoolant formulations as cavitation-erosion corrosion inhibitors toprovide prolonged protection to the aluminum surfaces in cooling and/orheating systems, such as the aluminum components of water pumps used ininternal combustion engines.

BACKGROUND OF THE INVENTION

Corrosion has long been a problem when certain metals or alloys are usedin applications in which they come into contact with an aqueous medium.For example, in heat-transfer systems, such as those found in internalcombustion engines, alcohol-based heat transfer fluids (i.e.,antifreezes can be very corrosive to the metal surfaces of theheat-transfer systems. Compounding this problem is that the corrosion isaccelerated under normal engine operating conditions (i.e., hightemperatures and pressures).

Aluminum surfaces, are particularly susceptible to corrosion. See Dardenet al., "Monobasic/Diacid Combination as Corrosion Inhibitors inAntifreeze Formulations," Worldwide Trends in Engine Coolants, CoolingSystem Materials and Testing, SAE Int'l SP-811, Paper #900804, pp.135-51 (1990)("SAE SP-811").

Indeed, aluminum surfaces are susceptible to several types of corrosionincluding general corrosion, pitting and crevice corrosion as well ascavitation-erosion corrosion. These types of corrosion, however,typically occur under different conditions and thus, affect differenttypes of aluminum surfaces. For example, general corrosion usuallyoccurs on aluminum surfaces which are readily susceptible to corrosionbecause they are poorly inhibited or because they are, subject to"heat-rejecting" conditions (e.g., cylinder heads and engine blocks) or"heat-accepting" conditions (e.g., radiators and heater cores).

Pitting/crevice corrosion usually occurs on the thin aluminum sheetsused in radiators or heater cores. Such corrosion generally results fromlocalized penetration of the oxide film which would otherwise cover andprotect the aluminum surfaces. See SAE SP-811.

Cavitation-erosion corrosion ("CE-type" corrosion), like pitting/crevicecorrosion, attacks the protective oxide film but results from explosionof bubbles on the aluminum surfaces. See SAE SP-811 at 136 CE-typecorrosion can be accelerated by the formation of foam in the coolingsystem. Foam results from air bubbles which are entrapped and agitatedin the cooling system. See, e.g., Nalco, "Cooling System Liner/WaterPump Pitting," Technifax TF-159 (1988). Thus, water pumps, which areused to circulate antifreeze coolants throughout a vehicle's coolingand/or heating systems, are particularly susceptible to CE typecorrosion. This is because bubbles are readily formed on the trailingsides of the water pump impeller blades due to locally reduced pressureand consequent boiling caused by the high rotation rate. When thesebubbles collapse in higher pressure areas in the water pump, they canerode the metal in these areas. This process can eventually destroy theimpeller causing loss of pumping performance and/or can perforate thepump body leading to loss of engine coolant. See, e.g., B. D. Oakes,"Observation on Aluminum Water Pump Cavitation Tests," Second Symposiumon Engine Coolants, ASTM STP 887, pp. 231-48 (1986).

The corrosion of aluminum surfaces has become a significant concern inthe automotive industry because of the increasing use of suchlightweight materials. See, e.g., Ward's Auto World, p. 22 September,1996); Ward's 1996 Automotive Yearbook, p. 27 (58th ed. 1996). Forexample, heat exchangers in cars and light duty trucks are now beingconstructed using aluminum components including the water pumps. SeeHudgens et al., "Test Methods for the Development of SupplementalAdditives for Heavy-Duty Diesel Engine Coolants," Engine CoolantTesting: Second Volume, ASTM STP 887, R. E. Beal, Ed., ASTM,Philadelphia, 1986, pp. 189-215; Oakes, B. D., "Observations on AluminumWater Pump Cavitation Tests," Engine Coolant Testing: Second Volume,ASTM STP 887, R. E. Beal, Ed., ASTM, Philadelphia, 1986, pp. 231-248;Beynon et al., "Cooling System Corrosion in Relation to Design andMaterials," Engine Coolant Testing: State of the Art, ASTM STP 705, W.H. Ailor, Ed., ASTM, Philadelphia, 1980, pp. 310-326. In particular,CE-type corrosion has become a significant concern because, aside frommechanical seal failures caused by high thermal stresses and inadequatelubrication, CE-type corrosion is one of the leading causes of waterpump failures. See, e.g., E. Beynon, supra at 310-326 (1980).

In general, corrosion inhibitors have been used to protect the metalsurfaces used in heat transfer systems. For example, triazoles,thiazoles, borates, silicates, phosphates, benzoates, nitrates, nitritesand molybdates have been used in antifreeze formulations. See, e.g.,U.S. Pat. No. 4,873,011; see also, SAE SP-811 at pp. 135-138, 145-46.However, such corrosion inhibitors have several problems, includingexpense, and inadequate long-term protection. See U.S. Pat. No.4,946,616, col. 1, lines 31-45; U.S. Pat. No. 4,588,513, col. 1, lines55-64; SAE SP-811, pp. 137-38. Accordingly, automobile manufacturershave begun using, and several now require, organic acid based (orextended life) corrosion inhibitors such as mono- and/or di-carboxylicacids. A number of carboxylic acid corrosion inhibitors have beendescribed. See, e.g., U.S. Pat. Nos. 4,382,008, 4,448,702 and 4,946,616;see also, U.S. Pat. application Ser. No. 08/567,639, incorporated hereinby reference.

However, carboxylic acid corrosion inhibitors, while effective atprotecting against general and pitting/crevice types of aluminumcorrosion, are generally ineffective as CE-type corrosion inhibitors.See, e.g. D. E. Turcotte, "Engine Coolant Technology, Performance andLife for Light Duty Application," Fourth Symposium on Engine Coolants(1997). Indeed, many of the known aluminum corrosion inhibitors, whileeffective at protecting against one or more types of aluminum corrosion,are generally not known to be effective at inhibiting all types ofaluminum corrosion. For example, silicates and phosphate salts known tobe effective at inhibiting general corrosion and CE-type corrosion, arenot known to inhibit polymerizable/crevice corrosion. Also, nitrateswhich are known to be effective pitting/crevice or CE-type corrosioninhibitors, are not known to inhibit general or CE-type corrosion.Similarly, polymeriable-acid graft copolymers have been used intraditional antifreeze formulations (i.e., containing silicates,phosphates and/or borates) as general corrosion inhibitors for theprotection of heat-rejecting aluminum surfaces. See U.S. Pat. Nos.4,392,972 and 4,904,114. However, such grafted copolymers are not knownto be effective as pitting/crevice or CE-type corrosion inhibitors.

Other polymeric compound have been suggested as CE-type corrosioninhibitors for aluminum and aluminum alloys. For example, U.S. Pat. No.5,288,419 discloses the use of a certain class of polymericpolycarboxylates as CE-type corrosion inhibitors. However, it has beenshown that such polymeric polycarboxylates do not consistently pass ASTMstandards for CE-type corrosion inhibitors.

Moreover, while other CE-type corrosion inhibitors are known, many ofthese corrosion inhibitors are metal-specific for non-aluminum surfaces,or are undesirable or unacceptable for the organic acid based antifreezeformulations used today. For example, silicates and phosphate salts,known CE-type corrosion inhibitors of aluminum surfaces, areunacceptable because they have been prohibited for use in organic acidformulations by a number of original equipment automotive manufacturers.See, e.g., General Motors Engineering Standards, "Long-Life AutomotiveEngine Coolant Antifreeze Concentrate-Ethylene Glycol," SpecificationNo. GM 6277M; Ford Engineering Material Specifications, "Coolant,Organic Additive Technology, Concentrate," Specification No.WSS-M97B44-C; Chrysler Corporation Engineering Standards, "EngineCoolant-Glycol Type-Inhibited-Production and Service Use," Standard No.MS-9769. See also, U.S. Pat. No. 4,146,488 (discloses the use of blendsof monoethanolamine borate and graft copolymer salts as effective inproviding cast iron corrosion protection).

Thus, there remains a need for an effective and reliable method ofinhibiting CE-type corrosion of aluminum surface which is compatiblewith the use of carboxylic acid based antifreeze formulations.

SUMMARY OF THE INVENTION

The present invention provides a method of inhibiting CE-type corrosionof aluminum surfaces. The inventive method comprises the step ofcontacting the aluminum surface with a corrosion inhibitor compositioncomprising a carboxylic acid, or salt, isomer or mixture thereof, and apolymerizable-acid graft polymer.

The carboxylic acid used in the corrosion inhibitor composition may beselected from the group consisting of saturated and unsaturatedaliphatic, and aromatic, mono-, di- and tri-carboxylic acids, andinorganic and organic salts and isomers thereof, and any combinationthereof. The polymelizable-acid graft polymer comprises up to 60% (byweight) of an unsaturated grafting acid and a base polymer comprising analkylene oxide polymer or mixtures thereof (i.e., forming copolymers),having the following formula:

    R"--[(OC.sub.n H.sub.2n).sub.z OR'].sub.a

wherein

each R' is independently selected from the group consisting of ahydrogen atom, hydrogen radicals and acyl radicals free of aliphaticunsaturation;

R" is selected from the group consisting of a hydrogen atom, hydrogenradicals, amine-containing radicals and acyl radicals;

each "n" has, independently, a value of from 2 to 4;

each "z" has, independently, a value of from 4 to about 3500;

"a" has a value of from 1 to 4.

Generally, the alkylene oxide polymers useful in this invention have anumber average molecular weight of from about 150 to about 380,000, andmore preferably from about 400 to about 10,000.

The method of this invention has been demonstrated to be a surprisinglyeffective means to inhibit CE-type corrosion of aluminum surfaces,especially those found in the cooling and/or heating systems of internalcombustion engines such as the water pumps used to circulate coolantthroughout the engine. For this application, the method involvescontacting the aluminum surface with an antifreeze formulationcomprising a liquid alcohol which functions as a freezing pointdepressant, from about 0.1% to about 5.5% by weight of the corrosioninhibitor composition, and from about 10% to about 90% by weight water.

DETAILED DESCRIPTION OF THE INVENTION

In order that the invention herein described may be more fullyunderstood, the following detailed description is set forth.

The present invention provides an effective and reliable method forinhibiting CE-type corrosion of aluminum surfaces. The inventive methodcomprises the step of contacting the aluminum surface with a corrosioninhibitor composition comprising (a) one or more carboxylic acids, orsalts or isomers thereof; and (b) one or more polymerizable-acid graftpolymers.

The carboxylic acid used in the corrosion inhibitor composition may beselected from the group consisting of saturated and unsaturatedaliphatic and aromatic mono-, di- and tri-carboxylic acids, andinorganic and organic salts (e.g., alkali and alkaline earth metal,ammonium and amine salts) and isomers thereof and any combinationthereof. Preferred carboxylic acids include C₄ -C₁₂ mono- ordi-carboxylic acids such as 2-ethyl hexanoic acid, neooctanoic acid,neodecanoic acid and sebacic acid, or salts (e.g., alkali and alkalineearth metal, ammonium or amine salts), isomers or mixtures thereof. Morepreferred carboxyic acids include mixtures having a major amount of a C₈mono-carboxylic acid component (e.g., neo-octanoic acid and/or 2-ethylhexanoic acid, more preferably 2-ethyl hexanoic acid) and neodecanoicacid, or salts (e.g., alkali and alkaline earth metal, ammonium or aminesalts) or isomers thereof. Where the mixture of a C₈ mono-carboxylicacid component and neodecanoic acid is used, the preferred mixturecomprises the C₈ mono-carboxylic acid component and neodecanoic acid inthe weight ratio of about 3:1. See U.S. Pat. application Ser. No.08/567,639, incorporated herein by reference.

The polymerizable-acid graft component of the corrosion inhibitorcomposition comprises an unsaturated grafting acid and an alkylene oxidepolymer having the following formula:

    R"--[(OC.sub.n H.sub.2n).sub.z OR'].sub.a

wherein:

each R' is independently selected from the group consisting of ahydrogen atom, hydrogen radicals, and acyl radicals free of aliphaticunsaturation;

R" is selected from the group consisting of a hydrogen atom, hydrogenradicals, amine-containing radicals and acyl radicals;

each "n" has, independently, a value of from 2 to 4;

each "z" has, independently, a value of from 4 to about 3500 andpreferably is from about 8 to about 800;

"a" has a value of from 1 to 4.

Generally, the alkylene oxide the polymers useful in this invention havea number average molecular weight of from about 150 to about 380,000,and more preferably from 400 to about 10,000.

The preferred class of alkylene oxide polymers have the formula:##STR1## wherein R is selected from the group consisting of a hydrogenatom, hydrogen radicals, amine-containing radials and acyl radicals;

each R' is independently selected from the group consisting of --H,--CH₃and --C₂ H₅, resulting, respectively, in an ethylene oxide ("EO"),propylene oxide ("PO") or butylene oxide ("BO") polymer; and

"z" has a value of from 4 to about 3500 and preferably is from about 8to about 800.

More preferred alkylene oxide polymers include copolymers of EO and POpolymers where the weight ratio of EO:PO can be from about 1:100 toabout 100:1, preferably from about 1:20 to about 20:1, and morepreferably from about 1:3 to about 3:1. Such alkylene oxide polymers arereadily available (e.g., Union Carbide's UCON®, Dow's, BASF's and Olin'spolyalkylene glycols) or readily made (see, e.g., U.S. Pat. Nos.4,146,488; 4,392,972 and 4,404,114).

The grafting acid may be any unsaturated, polymerizable-acid andselected from the group consisting of acrylic, methacrylic, crotonic,maleic, vinylsulfonic and vinyl phosphoric acids. The term"polymerizable-acid" refers to hydrolyzable precursors such asacrylonitrile, ethyl acrylate, methylmethacrylate, ethyl maleate,bis-(2-chloroethyl)vinylphosphonate, bis-(2-chloroethyl)vinylsulfonateor mixtures thereof and the like. Preferred grafting acids includeacrylic, methacrylic, crotonic and maleic acids, more preferably acrylicand maleic acids, and most preferably acrylic acid.

The grafting of the polymerizable-acid onto the alkylene oxide polymercan be carried out by free radical polymerization as is known in the art(see, e.g., U.S. Pat. Nos. 4,146,488, 4,392,972, 4,404,114 and4,528,334) such that the amount of grafting acid in the grafted polymeris up about 60% (by weight). Preferably the grafting acid content isfrom about 1.0% to, about 30%, more preferably from about 1% to about20%, and even more preferably from about 3% to about 15%. While evenvery small amounts of grafting acid are expected to provide CE-typecorrosion inhibition to the corrosion inhibitor composition used in thisinvention, the use of a grafted polymer having more than about 60%grafting acid content may result in a polymer having an unduly highviscosity.

The polymerizable-acid grafted polymers useful in the present inventionare preferably partially or wholly neutralized with a base to result inthe salt form of the grafted polymer. It is preferred that the acidgraft polymers be wholly neutralized. The base used to partially orwholly neutralize the grafted polymer may be any commercially availablebase including ammonium hydroxide, alkali metal or alkaline earth metalhydroxides, and amines including amines having the formula: ##STR2##wherein each R is, independently, H or an alkyl group having 1 to 6carbon atoms;

each of R₁, R₂ and R₃ is independently selected from the groupconsisting of alkylene radicals having 2 to 4 carbon atoms;

"e" has a value of from 0 to 3

each of "b," "c" and "d" is independently 0 or 1, with the proviso thatwhen "b," "c" and "d" are 1, then "e" is 0.

When alkali metal or alkaline earth metal hydroxides are used, sodium orpotassium hydroxide, or mixtures thereof are preferred.

The present method may be used in a number of CE-typecorrosion-inhibiting applications, including, but not limited to,antifreeze coolant concentrates and formulations (diluted concentrates)used in the cooling systems of internal combustion engines and inindustrial and commercial heating and/or cooling systems. One preferredapplication of this method is to inhibit CE-type corrosion of thealuminum components of the cooling systems of internal combustionengines such as the water pumps of those systems.

When used in antifreeze concentrates, such concentrates typicallycomprise (a) a liquid alcohol which functions as a freezing pointdepressant and (b) a corrosion inhibitor composition comprising acarboxylic acid, or salt, isomer or mixture thereof and apolymerizable-acid graft polymer. To form an antifreeze formulation, theconcentrate is diluted with water such that, e.g., the formulationcomprises from about 10% to about 90% by weight water, and morepreferably from about 25% to about 75% by weight water.

Suitable liquid alcohols which function as freezing point depressantsinclude any alcohol or other heat transfer medium and preferably is atleast one alcohol, selected from the group consisting of methanol,ethanol, propanol, ethylene glycol, diethylene glycol, triethyleneglycol, propylene glycol, dipropylene glycol, butylene glycol, glycerol,the monoethylether of glycerol, the dimethylether of glycerol, alkoxyalkanols (such as methoxyethanol) and mixtures thereof. The preferredalcohol is selected from the group consisting of ethylene glycol,diethylene glycol, propylene glycol, dipropylene glycol and mixturesthereof.

The corrosion inhibitor con position is typically added in an amountsufficient such that from about 0.1% to about 5.5% (by weight) of thecorrosion inhibitor composition is present in the antifreeze coolantconcentrate. The carboxylic acid and polymerizable-acid graft polymerused in the corrosion inhibitor composition are described above. Morepreferably, the carboxylic acid comprises a mixture of a major amount ofa C₈ mono-carboxylic acid component (e.g., neo-octanoic acid and/or2-ethyl hexanoic acid, more preferably 2-ethyl hexanoic acid) andneo-decanoic acid. Where the mixture of a C₈ mono-carboxylic acidcomponent and neo-decanoic acid is used, the preferred mixture comprisesthe C₈ mono-carboxylic acid component and neo-decanoic acid in theweight ratio of about 3:1 (e.g., from about 2.4% to about 3.3% (byweight of the antifreeze coolant concentrate) of the C₈ mono-carboxylicacid component, more preferably about 3.1%, and from about 0.8% to about1.1% (by weight of the antifreeze coolant concentrate) of neo-decanoicacid, more preferably about 1.0%). See U.S. Pat. application Ser. No.08/567,639.

The amount of the grafted polymer present may be from about 0.01 toabout 20% (by weight of the antifreeze coolant concentrate) and morepreferably from about 0.1% to about 10%.

One preferred antifreeze coolant formulation useful in the presentinvention comprises:

(a) from about 80% to about 99% by weight of a liquid alcohol whichfunctions as a freezing point depressant;

(b) from about 2.0% to about 5.0% by weight of a mixture of2-ethylhexanoic acid, or salts or isomers thereof, and neo-decanoicacid, or salts or isomers thereof,

(c) from about 0.01% to about 20 (by weight) of a polymerizable-acidgraft polymer comprising (i) acrylic acid and (ii) an alkylene oxidecopolymer comprising a EO and PO polymers; and

(d) from about 10% to about 90% by weight water.

The grafted copolymers herein described have previously been identifiedas lubricants as well as general corrosion inhibitors used intraditional antifreeze formulations (i.e., containing silicates,phosphates and/or borates) to protect heat-rejecting aluminum surfaces.See, e.g., U.S. Pat. Nos. 4,146,488; 4,392,972 and 4,404,114. However,such grafted copolymers have not previously been recognized as, orsuggested to be, CE-type corrosion inhibitors for aluminum surfaces.

The corrosion inhibitor con position may also include from about 0.01%to about 0.4% (by weight of the antifreeze coolant concentrate) of oneor more alkali, alkaline earth metal, ammonium or amine salts ofnitrite. Additionally, the corrosion inhibitor composition may alsoinclude one or more inorganic and/or organic corrosion inhibitors, suchas di-carboxylic acids, triazoles, thiazoles, phosphates, borates,silicates, molybdates, nitrates or the alkali metal, alkaline earthmetal, ammonium or amine salts thereof. Such additional corrosioninhibitors may be added in concentrations of up to about 5.5% (by weightof the total antifreeze formulation). The preferred corrosion inhibitorcomposition used in this invention further comprises a triazole orthiazole, more preferably, an aromatic triazole or thiazole such asbenzotriazole ("BZT"), mercaptobenzothiazole ("MBT") or tolyltriazole("TTZ") and most preferably, TTZ.

The antifreeze formulation i nay also comprise a sufficient amount of analkali metal hydroxide to adjust the pH to between about 6.0 to about9.5, preferably to about 6.5 to about 9.0. Other additives may also beused depending on the application. Suitable additives include dyes(e.g., "Alizarine Green," "Uranine Yellow" or "Green AGS-liquid" fromAbbey Color Inc., "Orange II (Acid Orange 7)" or "Intracid Rhodamine WT(Acid Red 388)" from Crompton & Knowles Corp.), odor masking aids,perfumes, antifoams, rust inhibitors, pH buffers, scale inhibitors,and/or sequestration and dispersion agents (e.g.,"Dequest" from MonsantoChemical Company, "Bayhibit" from Miles Inc., "Nalco" or "NalPREP" fromNalco Chemical Company). Also, although the grafted copolymers describedherein have been shown to be useful as lubricants (see, e.g., U.S. Pat.No. 4,146,488), and thus capable of reducing water pump seal failurescaused by high thermal stresses on the seal interfaces (resulting fromexcessive frictional heating), additional lubricants may also be addedas necessary (e.g., preferably fluorinated polymers such as TEFLON®,KRYTOX®, VYDAX® from Du Pont).

In order that this invention may be better understood, the followingexamples are set forth. These examples are for the purpose ofillustration only and are not to be construed as limiting the scope ofthe invention in any way.

EXAMPLES

To evaluate the effectiveness of the polymerizable-acid graft polymersas CE-type corrosion inhibitors, a number of formulations were subjectedto standard analytical tests. In each of these formulations, one of fivestock antifreeze coolants were used (Concentrates A-D and Formulation).Concentrates A-D (Tables 1A-1D) are commercially available and/orindustry standard antifreeze coolant concentrates ("GM-6043M" (A),Texaco's "Extended Long Life Coolant DEXCOOL®" (B), Prestone's "ExtendedLife 5/100 Antifreeze" (C), and "GM-6038M" (D)). Formulation E is a usedcoolant formulation comprising a 50/50 (by volume) blend of deionizedwater and Concentrate A that was subjected to a flee test of 100,000miles. As a result of the fleet test, Formulation E also comprisescertain degradation and corrosion products (e.g., glycolate, acetate,formate).

                  TABLE 1A                                                        ______________________________________                                        Stock Antifreeze Coolant Concentrate "A"                                      Components              wt %                                                  ______________________________________                                        Ethylene glycol         95.53                                                 Sodium nitrate (NaNO.sub.3)                                                                           0.10                                                  Sodium molybdate (Na.sub.2 MoO.sub.4.2H.sub.2 O)                                                      0.20                                                  Sodium tetraborate (Na.sub.2 B.sub.4 O.sub.7.5H2O)                                                    0.40                                                  Sodium silicate (liquid Na.sub.2 SiO.sub.3)                                                           0.30                                                  (SiO.sub.2 /Na.sub.2 O weight-ratio of 3.22)                                  Phosphoric acid (83% H.sub.3 PO.sub.4)                                                                0.15                                                  Sodium mercaptobenzothiazole (50% soln.)                                                              0.50                                                  Sodium tolyltriazole (50% soln.)                                                                      0.20                                                  Sodium hydroxide        0.235                                                 Miscellaneous (water, stabilizers, dyes, etc.)                                                        2.385                                                 pH                      10.5                                                  ______________________________________                                    

                  TABLE 1B                                                        ______________________________________                                        Stock Antifreeze Coolant Concentrate "B"                                      Components             wt %                                                   ______________________________________                                        Ethylene glycol, diethylene glycol                                                                   >91.8                                                  and m-butylether-di(ethylene glycol)                                          Sebacic acid           0.23                                                   2-ethyl hexanoic acid  2.74                                                   Potassium tolyltriazole (0.25 wt % soln.)                                                            2195                                                                          (mg/ml)                                                pH                     8.9                                                    ______________________________________                                    

                  TABLE 1C                                                        ______________________________________                                        Stock Antifreeze Coolant Concentrate "C"                                      Components           wt %                                                     ______________________________________                                        Ethylene and diethylene glycol                                                                     >80                                                      Disodium sebacate    1-5                                                      Miscellaneous (NaTTZ, NaNO3)                                                                       >1                                                       pH                   9.0                                                      ______________________________________                                    

                  TABLE 1D                                                        ______________________________________                                        Stock Antifreeze Coolant Concentrate "D"                                      Components              wt %                                                  ______________________________________                                        Ethylene glycol         95.76-                                                                        95.77                                                 Sodium nitrate (NaNO.sub.3)                                                                           0.20                                                  Sodium tetraborate (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O)                                              1.00                                                  Sodium metasilicate (Na.sub.2 SiO.sub.3.5H.sub.2 O)                                                   0.15                                                  Sodium orthophosphate (Na.sub.3 PO.sub.4.12H.sub.2 O)                                                 0.45                                                  Sodium tolyltriazole (50% soln.)                                                                      0.20                                                  Sodium hydroxide        0.20                                                  Miscellaneous (water, stabilizers, dyes, etc.)                                                        2.032-                                                                        2.042                                                 pH                      10.5                                                  ______________________________________                                    

To these stock coolants were added a variety of non-grafted and graftedpolymer "additives" shown in Tables 2 and 3 with and without a pHadjustment (i.e., NaOH). For each of these additives, the base polymerused was either propylene oxide ("PO") or a copolymer of ethylene oxideand propylene oxide ("EO/PO").

                  TABLE 2                                                         ______________________________________                                        Non-Grafted Polymer Additives                                                                 Additive                                                      Characteristics   1       2          3                                        ______________________________________                                        Base polymer      PO      EO/PO,     PO                                                                 50/50 (v/v)                                         Number average molecular weight                                                                 910     5100       425                                      Starter alcohol   None    butanol    None                                     Polymerizable-acid graft polymer                                                                 0        0         0                                       (% graft)                                                                     Grafted acid      None    None       None                                     pH adjusted with NaOH                                                                           None    None       None                                     ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Grafted Polymer Additives                                                                      Additive                                                     Characteristics    4          5                                               ______________________________________                                        Base polymer       EO/PO,     EO/PO,                                                             50/50 (v/v)                                                                              50/50 (v/v)                                     Number average molecular weight                                                                  5100       5100                                            Starter alcohol    butanol    None                                            Polymerizable-acid graft polymer                                                                  15         15                                             (% graft)                                                                     Grafted acid       Acrylic    Acrylic                                         pH Adjusted with NaOH to pH = 7                                                                  No         Yes                                             ______________________________________                                    

As discussed below in more detail, the resulting solutions were thensubjected to any of four tests.

1. ASTM D2809--"Standard Test Method for Cavitation Corrosion andErosion-Corrosion Characteristics of Aluminum Pumps with EngineCoolants"

Fourteen different antifreeze, formulations were prepared and evaluatedunder the conditions set forth by ASTM D 2809. See Annual Book of ASTMStandards, Section 15, Volume 15.05, (1996), incorporated herein byreference. ASTM D2809 is the standard test method for CE-type corrosionof aluminum pumps using antifreeze coolants. As set forth in Table 4,except for Examples 1, 5 and 9 which serve as control formulations, eachof the Examples tested comprised a stock antifreeze coolant(Concentrates B or D shown in Tables 1B-1D, respectively), and 0.5% (byweight) of a polymer additive. Before testing, each of the testsolutions was diluted in accordance with ASTM D2809. These formulationswere prepared in accordance with note #4 set forth in ASTM D2809.

After preparing the formulations and subjecting them to the testprocedures set forth in ASTM D2809 (100 hours of pump operation at anominal pump speed of 4600 rpm, 113° C. and 103 kPa), the aluminum pump,casting/cover and impeller were visually inspected and rated on a scaleof 1 to 10 (according to the recommendations set forth in ASTM D2809. Arating of 8 (for each of the pump, casting/cover and impeller) is theminimum required to pass ASTM D2809 with 10 being perfect.

                  TABLE 4                                                         ______________________________________                                        Cavitation-Erosion Corrosion (ASTM D2809)                                            Stock Coolant                                                                            Additive Pump   Casting                                                                             Impeller                              Example                                                                              Used       Used     Rating Rating                                                                              Rating                                ______________________________________                                        1      B          None     4      5     1                                     2      B          1        8      7     5                                     3      B          4        10     10    9                                     4      B          5        10     10    10                                    5      C          None     6      5     5                                     6      C          1        7      7     7                                     7      C          4        8      8     7                                     8      C          5        10     10    10                                    9      D          None     1      2     1                                     10     D          1        5      8     5                                     11     D          2        8      8     6                                     12     D          3        7      8     7                                     13     D          4        8      10    8                                     14     D          5        9      9     9                                     ______________________________________                                    

As shown in Table 4, the control formulations (Examples 1, 5 and 9) allfailed ASTM D2809. The formulations with non-grafted polymer additives(Examples 2, 6, 10-12) also failed ASTM D2809. However, the use of agrafted polymer improved performance in all formulations and with oneexception (Example 7, and even that formulation demonstrated improvedperformance compared to Examples 5-6), resulted in an antifreezeformulation that consistently passed ASTM D2809 (Examples 3-4, 8,13-14). Moreover, the use of a grafted polymer that had been neutralizedwith a base (Examples 4, 8 and 14) demonstrated the highest overallrating of the formulations tested, and indeed for two of the three stockcoolants achieved a perfect score.

2. ASTM D1881--"Standard rest Method for Foaming Tendencies of EngineCoolants in Glassware"

Six different antifreeze formulations were prepared and evaluated underthe conditions set forth by ASTM D1881. See Annual Book of ASTMStandards, Section 15, Volume 15.05 (1996), incorporated herein byreference. ASTM D1881 is a standard test method used to evaluate thefoaming tendencies of antifreeze coolants under laboratory controlledaeration conditions. As previously discussed, the foaming of anantifreeze formulation in a vehicle's cooling and/or heating systemaccelerates CE-type corrosion.

As set forth in Table 5, all of the Examples tested comprisedConcentrate A. Examples 15-18 include 0.5% (by weight) of differentcommercially available water pump treatment additives. Example 19comprised 0.5% (by weight) of a non-grafted polymer while Example 20comprised 0.5% (by weight) of a neutralized grafted polymer. Beforetesting, each of the solutions was (diluted in accordance with ASTMD1881. The additive concentration should be diluted with deionized waterto the recommended use concentration (at freezing point of ±17.8° C.±1°C. or 0° F. ±2° F.) These formulations were prepared in accordance withthe "Treatment of Mixtures" prescribed by ASTM D1176.

After preparing the test formulations and subjecting them to theprocedures set forth in ASTM D1881, § 8, the foam volume and the breaktime were measured according to ASTM D1881. The maximum allowed to passASTM D1881 is a foam volume of 150 ml and a break time of 5 seconds.

                  TABLE 5                                                         ______________________________________                                        Anti-Foaming Properties (ASTM D1881)                                                 Stock                   Foam  Foam                                            Coolant Additive        Volume                                                                              Break Time                               Example                                                                              Used    Used            (ml)  (sec)                                    ______________________________________                                        15     A       Water Pump Lubricant &                                                                        >500  120                                                     Rust Inhibitor                                                                (Kleen-Flo ®)                                              16     A       STP Radiator Anti Rust                                                                        >500  150                                                     plus Water Pump Lube                                                          (First Brands Corp.)                                           17     A       Prestone Cooling System                                                                       >500  130                                                     Anti Rust plus Water                                                          Pump Lubricant                                                                (Prestone Products Corp.)                                      18     A       Radiator Antioxidant,                                                                         >500  50                                                      Antirust and Lubricant                                                        (Bardahl Co.)                                                  19     A       1               50    5                                        20     A       5               45    4                                        ______________________________________                                    

As shown in Table 5, only Examples 19 and 20 passed both ASTM D1881standards and Example 20 (comprising a rafted pH-adjusted polymer) hadthe best performance of all formulations tested.

3. ASTM D4340--"Standard Test Method for Corrosion of Cast AluminumAlloys in Engine Coolants under Heat-Rejecting Conditions"

Six different antifreeze formulations were prepared and evaluated underthe conditions set forth by ASTM D4340 See Annual Book of ASTMStandards, Section volume 15.05, (1996), incorporated herein byreference. ASTM D4340 is a standard method for general corrosion ofaluminum surfaces under heat-rejecting conditions heat-transferconditions present in aluminum cylinder heads).

As set forth in Table 6, except for Examples 21 and 24 which served ascontrol formulations, each of these examples comprised a stockantifreeze coolant (Concentrate B or Formulation E shown it Tables 1Band 1E, respectively) and 0.5% (by weight) of a polymer additive(additive 1 or 5 shown in Tables 2-3). Before testing, each of thesolutions was diluted with "aggressive water" (750 ml. of deionizedwater containing 165 mg. of reagant grade NaCl) to make a formulationwith 25% (by volume) concentrate. These formulations were prepared inaccordance with the "Treatment of Mixtures" prescribed by ASTM D1176.

After preparing the formulations and subjecting them to the testprocedures set forth in ASTM D4340 (the aluminum specimen is exposed for168 hours to the antifreeze formulation and maintained at a temperatureof 135° C., pressure of 193 kPa), the corrosion rate was measured(average, of duplicate specimens). The maximum corrosion rate allowed byASTM D4340 is 1.0 mg/cm² /week.

                  TABLE 6                                                         ______________________________________                                        Aluminum Hot Surface Test (ASTM D4340)                                        Stock    Coolant       Additive Corrosion Rate                                Example  Used          Used     (mg/cm.sup.2 /week)                           ______________________________________                                        21       B             None     1.0                                           22       B             1        0.0                                           23       B             5        0.0                                           24       E             None     9.9                                           25       E             1        3.8                                           26       E             5        1.8                                           ______________________________________                                    

As shown in Table 6, the addition of a grafted polymer (Examples 23 and26) resulted in the lowest corrosion rate of all the formulationstested. While the addition of a non-grafted polymer to Coolant B(example 22) demonstrated the same corrosion rate (0.0) as that for theformulation with a grafted polymer (Example 23), because the corrosionrate of the corresponding control formulation (Example 21) was alreadyrelatively low, no conclusions can be made regarding the effectivenessof the non-grafted polymer compared to the grafted polymer. However, thesignificant improvement in corrosion rate (i.e., decreased rate) by theaddition of a grafted polymer was demonstrated for Formulation E, i.e.,the used formulation that was subjected to a fleet test of 100,000 miles(Examples 24-26). These results suggest that the grafted polymersprovide improved protection against general aluminum corrosion for bothsilicate-based antifreeze formulations as well as organic acid basedformulations.

4. ASTM D1384--"Standard Test Method for Corrosion Test for EngineCoolants in Glassware"

Ten different antifreeze formulations were prepared and evaluated underthe conditions set forth by ASTM D1384. See Annual Book of ASTMStandards, Section 15, Volume 15.05 (1996), incorporated herein byreference. ASTM D1384 is a standard test method for general corrosion ofa variety of metals typically found in the cooling and/or heatingsystems of internal combustion engines. In addition to the requiredmetals to be tested under ASTM D1384, a high lead solder specimen wasalso tested.

As set forth in Table 7, except for Examples 27, 31 and 34 which servedas control formulations, each of these examples comprised a stockantifreeze coolant (Concentrates B or C, or Formulation E shown inTables 1B, 1C and 1E, respectively) and 0.5% (by weight) of a polymeradditive (additive 1, 4 or 5 shown in Tables 2-3). Before testing, eachof the solutions was diluted with "corrosive water" (deionized watercontaining 100 ppm each of deionized water containing 100 ppm each ofSO₄ ²⁻, HCO₃ ⁻ and Cl⁻, all added as Na salts) to make a formulationwith 33.3% (by volume) concentrate. These formulations were prepared inaccordance with the "Treatment of Mixtures" prescribed by ASTM D1176.

After preparing the formulations and subjecting them to the testprocedures set forth in ASTM D1384 (the metal specimens were immersedfor 336 hours in the antifreeze formulation and maintained at atemperature of 88° C.), the weight change of the metal specimens weremeasured (average of triplicate specimens). A negative weight losssignifies a weight increase due to the formation of a protective coatingon the metal surfaces.

                                      TABLE 7                                     __________________________________________________________________________    Metal Weight Loss (mg) (ASTM D1384)                                                Stock Coolant                                                                        Additive                                                                           High Lead                                                                              ASTM                                                Example                                                                            Used   Used Solder                                                                             Copper                                                                            Solder                                                                            Brass                                                                            Steel                                                                            Cast Iron                                                                          Aluminum                             __________________________________________________________________________    ASTM             --   10  30  10 10 10   30                                   Standard                                                                      27   B      None 240  2.3 1.8 2.7                                                                              1.2                                                                              -0.8 -1.5                                 28   B      1    140  -0.8                                                                              -1.3                                                                              -0.1                                                                             -1.5                                                                             -4.7 -3.0                                 29   B      4    -108 -1.4                                                                              16  -1.8                                                                             -0.1                                                                             -3.1 -3.0                                 30   B      5    -70  -1.5                                                                              -0.5                                                                              -1.3                                                                             -0.8                                                                             -3.5 -3.0                                 31   C      None 23.6 2.5 2.9 2.4                                                                              0.8                                                                              8.4  0.1                                  32   C      1    8.2  0.3 0.1 0.6                                                                              1.0                                                                              -1.1 -4.6                                 33   C      5    23   -1.5                                                                              -0.2                                                                              -1.4                                                                             -0.8                                                                             -5.8 -3.0                                 34   E      None 178.4                                                                              2.4 2.5 2.5                                                                              8.7                                                                              437.6                                                                              2.0                                  35   E      1    -33.3                                                                              -0.3                                                                              --1.3                                                                             -0.2                                                                             3.9                                                                              210.0                                                                              -3.9                                 36   E      5    -6.4 -2.0                                                                              -0.2                                                                              -0.6                                                                             -0.4                                                                             21.6 -4.3                                 __________________________________________________________________________

As Table 7 shows, the addition of a grafted polymer (Examples 29-30, 33,36) to the control formulations (Example. 27, 31, 34) improved (bydecreasing) the weight loss of the aluminum. Such result, confirm theability of the grafted polymers to serve as general corrosion inhibitersfor aluminum. In general, the results also show that such graftedpolymers are also effective general corrosion inhibitors for othermetals (see e.g., Example 27 vs. 28-29 and Example 34 vs. 35-36 for highlead solder, cast iron and steel).

What is claimed is:
 1. A method for inhibiting the cavitation-erosioncorrosion of aluminum surfaces comprising the step of contacting saidsurfaces with a formulation comprising a corrosion inhibitorcomposition, said corrosion inhibitor composition comprises (a) one ormore carboxylic acids, or salts thereof, and (b) a polymerizable-acidgraft polymer comprising from about 1.0% to about 60% by weight of anunsaturated grafting acid and an alkylene oxide polymer, saidpolymerizable-acid graft polymer having the following formula:

    R"--[(OC.sub.n H.sub.2n).sub.z OR'].sub.a

wherein each R' is independently selected from the group consisting of ahydrogen atom, hydrogen radicals and acyl radicals free of aliphaticunsaturation; R" is selected from the group consisting of a hydrogenatom, hydrogen radicals, amine-containing radicals and acyl radicals,provided that all the R' and R" groups are not, at the same time, ahydrogen atom; each "n" has, independently, a value of from 2 to 4; each"z" has, independently, a value of from 4 to about 3500; "a" has a valueof from 1 to 4and said formulation further comprising an alkali metalhydroxide in an amount sufficient to adjust the pH of the formulation tofrom 6.0 to 9.0.
 2. A method for inhibiting the cavitation-erosioncorrosion of aluminum surfaces comprising the step of contacting saidsurfaces with an antifreeze coolant formulation comprising:(a) a liquidalcohol which function is as a freezing point depressant; (b) from about0.1% to about 5.5% by weight of a corrosion inhibitor compositioncomprising (i) one or more carboxylic acids, or salts thereof, and (ii)a polymerizable-acid graft polymer comprising from about 1.0% to about60% by weight of an unsaturated grafting acid and an alkylene oxidepolymer, said polymerizable-acid graft polymer having the followingformula:

    R"--[(OC.sub.n H.sub.2n).sub.z OR'].sub.a

whereineach R' is independently selected from the group consisting of ahydrogen atom, hydrogen radicals, and acyl radicals free of aliphaticunsaturation; R" is selected from the group consisting of a hydrogenatom, hydrogen radicals, amine-containing radicals and acyl radicals,provided that all the R' and R" groups are not, at the same time, ahydrogen atom; each "n" has, independently, a value of from 2 to 4; each"z" has, independently, a value of from 4 to about 3500; "a" has a valueof from 1 to 4; (c) an alkali metal hydroxide in an amount sufficient toadjust the pH of the formulation to from 6.0 to 9.0, and (d) from about10% to about 9.0% by weight water.
 3. The method of either claims 1 or2, wherein the corrosion inhibitor composition comprises one or morecarboxylic acids selected from the group consisting of saturated andunsaturated, aliphatic and aromatic mono-, di- and tri-carboxylic acids,and salts, and mixtures thereof.
 4. The method of either claims 1 or 2,wherein the corrosion inhibitor composition comprises one or morecarboxylic acids selected from the group consisting of C₄ -C₁₂mono-carboxylic and di-carboxylic acids, and salts, and mixturesthereof.
 5. The method of either claims 1 or 2, wherein the corrosioninhibitor composition comprises one or more carboxylic acids selectedfrom the group consisting of 2-ethyl hexanoic acid, neooctanoic acid,neodecanoic acid, sebacic acid, and alkali and salts, and mixturesthereof.
 6. The method of either claims 1 or 2, wherein the corrosioninhibitor composition comprises a mixture comprising a major amount of aC₈ mono-carboxylic acid component, or salts, or isomers thereof, andneo-decanoic acid, or salts thereof.
 7. The method of either claims 1 or2, wherein the alkylene oxide polymer has the formula: ##STR3## whereinR is selected from the group consisting of a hydrogen atom, hydrogenradicals, amine-containing radicals, and acyl radicals;each R' isindependently selected from the group consisting of --H, --CH₃ and --C₂H₅, resulting, respectively, in an ethylene oxide ("EO"), propyleneoxide ("PO") or butylene oxide ("BO") polymer; and "z" has a value offrom 4 to about
 3500. 8. The method of claim 7, wherein the alkyleneoxide polymer is selected from the group consisting of EO and POpolymers, and copolymers of EO and PO polymers.
 9. The method of claim7, wherein the alkylene oxide polymer is a copolymer of EO and POpolymers having a weight ratio of from about 1:100 to about 100:1 ofEO:PO.
 10. The method of claim 7, wherein the alkylene oxide polymer isa copolymer of EO and PO polymers having a weight ratio of from about1:20 to about 20:1 of EO:PO.
 11. The method of claim 7, wherein thealkylene oxide polymer is a copolymer of EO and PO polymers having aweight ratio of from about 1:3 to about 3:1 of EO:PO.
 12. The method ofeither claims 1 or 2, wherein the unsaturated grafting acid is selectedfrom the group consisting of acrylic, methacrylic, crotonic, maleic,vinylsulfonic and vinylphosphoric acids.
 13. The method of either claims1 or 2, wherein the polymerizable-acid grafting polymer comprises fromabout 1.0% to about 30% of the grafting acid.
 14. The method of eitherclaims 1 or 2, wherein the polymerizable-acid graft polymer comprisesfrom about 1.0% to about 20% of the grafting acid.
 15. The method ofeither claims 1 or 2, wherein the formulation comprises from about 0.01%to about 20% by weight of the polymerizable-acid graft polymer.
 16. Themethod of either claims 1 or 2, wherein the formulation comprises fromabout 0.1% to about 10% by weight of the polymerizable-acid graftpolymer.
 17. The method of either claims 1 or 2, wherein thepolymerizable-acid grafting polymer comprises from about 3.0% to about15% by weight of the grafting acid.
 18. The method of claim 2, whereinthe liquid alcohol is selected from the group consisting of methanol,ethanol, propanol, ethylene glycol, diethylene glycol, triethyleneglycol, propylene glycol, dipropylene glycol, butylene glycol, glycerol,the monoethylether of glycerol, the dimethylether of glycerol, alkoxyalkanols, and mixtures thereof.
 19. The method of claim 2, wherein theliquid alcohol is selected from the group consisting of ethylene glycol,diethylene glycol, propylene glycol, dipropylene glycol, and mixturesthereof.
 20. The method of claim 2, wherein the antifreeze coolantformulation further comprises from about 0.01% to 0.4% by weight of oneor more alkali or alkaline earth metal, ammonium and amine salts ofnitrite.
 21. The method of claim 2, wherein the antifreeze coolantformulation further comprises one or more additional corrosioninhibitors selected from the group consisting of di-carboxylic acids,triazoles, thiazoles, phosphates, borates, silicates, molybdates,nitrates and the alkali or alkaline earth metal, ammonium and aminesalts thereof.
 22. The method of claim 2, wherein the antifreeze coolantformulation further comprises benzotriazole, mercaptobenzothiazole ortolyltriazole.
 23. The method of either claims 21 or 22, wherein theantifreeze coolant formulation comprises up to about 5.5% by weight ofthe additional corrosion inhibitors.
 24. The method of claim 2, whereinthe alkali mental hydroxide is present in an amount sufficient to adjustthe pH of the formulation to from 6.5 to 9.0.
 25. The method of claim 2,wherein the antifreeze coolant formulation further comprises one or moreadditives elected from the group consisting of dyes, odor maskingagents, perfumes, antifoaming agents, lubricants, rust inhibitors, pHbuffers, scale inhibitors, and sequestration and dispersion agents. 26.The method of claim 2, wherein the antifreeze coolant formulationcomprises from about 25% to about 75% by weight water.
 27. A method forinhibiting the cavitation-erosion corrosion of aluminum surfacescomprising the step of contacting said surfaces with an antifreezecoolant formulation comprising:(a) from about 80% to about 99% by weightof a liquid alcohol which functions as a freezing point depressant; (b)from about 2.0% to about 5.0 by weight of a mixture of 2-ethylhexanoicacid, or salts thereof, and neo-decanoic acid, or salts thereof, (c)from about 0.01% to about 20 of a polymerizable-acid graft polymercomprising (i) acrylic acid and (ii) an alkylene oxide polymercomprising a copolymer of EO and PO polymers; (d) from about 10% toabout 90% by weight water; and said formulation further comprising analkali metal hydroxide in an amount sufficient to adjust the pH of thformulation to from 6.0 to 9.0.